Phosphonoacetate and phosphonoformate were first synthesized in 1924 (Nylen, Chem. Berichte 57:1023); however, the ability of these compounds to inhibit viral enzymes selectively was not immediately demonstrated. Helgstrand, et al. Science 201:819-821 (Sep. 1, 1978) disclosed that both phosphonoacetic acid and phosphonoformic acid inhibit several DNA polymerases and preferentially inhibit several viral DNA polymerases. Phosphonoformate and phosphonoacetate are presently known to selectively inhibit the DNA polymerase of many viruses, including human cytomegalovirus (HCMV), herpes simplex virus (HSV) and the reverse transcriptase of human immunodeficiency virus (HIV). Chrisp and Clissold (1991) Drugs 41:104 review the pharmacology of these agents. Phosphonoacetate is too toxic for use in humans, but phosphonoformate (Foscavir, Astra) is approved for human use in HCMV-infected AIDS patients. However, it is not highly potent, requires prolonged intravenous administration and has substantial toxicity to the kidney and other organs. Ericksson, et al., U.S. Pat. Nos. 4,215,113; 4,339,445; 4,665,062; 4,771,041 teach the use of phosphonoformic acid as the selective agent in treating viral infections, including herpes virus type I and II and cytomegalovirus, in treating cancer caused by virus, and also opposing transformation of cells caused by oncogenic viruses.
Derivatized forms of phosphonoacids and pharmaceutical formulations comprising these compounds are known. U.S. Pat. No. 5,072,032 to McKenna discloses thiophosphonoacids; U.S. Pat. Nos. 4,386,081 and 4,591,583 to Helgstrand et al. disclose phosphonoformic acid esters of alkyl, alkylene, alkoxy and related cyclic and aromatic groups and some of these are shown to inhibit herpes virus and the functions and intracellular multiplication of influenza virus. U.S. Pat. No. 5,194,654 to Hostetler et al, discloses phospholipid derivatives of phosphonoacids, their incorporation into liposomes and their use as selective antiviral and antiretroviral agents.
There is a continuing need for less toxic, more selective and more effective antiviral prodrugs of the phosphonoacids.